Differential thermal ink jet printing mechanism

ABSTRACT

An ink jet nozzle assembly includes a nozzle chamber having an inlet receiving ink from a reservoir and a nozzle through which the ink can be ejected. The chamber includes a fixed portion and a movable portion configured for relative movement in an ejection phase and alternate relative movement in a refill phase. A pair of spaced apart actuating arms is connected with the movable portion and undergoes differential thermal expansion upon heating to effect periodically the relative movement. The inlet is positioned and dimensioned relative to the nozzle such that ink is ejected preferentially from the chamber through the nozzle in droplet form during the ejection phase, and ink is alternately drawn preferentially into the chamber from the reservoir through the inlet during the refill phase.

[0001] This is a C-I-P of application Ser. No. 09/112,754 as filed onJul. 10, 1998

FIELD OF THE INVENTION

[0002] The present invention relates to ink jet printing systems and, inparticular, discloses a thermally actuated slotted chamber wall ink jetprinter.

BACKGROUND OF THE INVENTION

[0003] Many different types of printing have been invented, a largenumber of which are presently in use. The known forms of print have avariety of methods for marking the print media with a relevant markingmedia. Commonly used forms of printing include offset printing, laserprinting and copying devices, dot matrix type impact printers, thermalpaper printers, film recorders, thermal wax printers, dye sublimationprinters and ink jet printers both of the drop on demand and continuousflow type. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

[0004] In recent years, the field of ink jet printing, wherein eachindividual pixel of ink is derived from one or more ink nozzles hasbecome increasingly popular primarily due to its inexpensive andversatile nature.

[0005] Many different techniques on ink jet printing have been invented.For a survey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

[0006] Ink Jet printers themselves come in many different types. Theutilisation of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electrostatic ink jetprinting.

[0007] U.S. Pat. No. 3,596,275 by Sweet also discloses a process ofcontinuous ink jet printing including the step wherein the inkjet streamis modulated by a high frequency electrostatic field so as to cause dropseparation. This technique is still utilized by several manufacturersincluding Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet etal)

[0008] Piezoelectric ink jet printers are also one form of commonlyutilized ink jet printing device. Piezoelectric systems are disclosed byKyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes adiaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970)which discloses a squeeze mode of operation of a piezoelectric crystal,by Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend modeof piezoelectric operation, by Howkins in U.S. Pat. No. 4,459,601 whichdiscloses a Piezoelectric push mode actuation of the ink jet stream andby Fischbeck in U.S. Pat. No. 4,584,590 which discloses a sheer modetype of piezoelectric transducer element.

[0009] Recently, thermal ink jet printing has become an extremelypopular form of ink jet printing. The ink jet printing techniquesinclude those disclosed by Endo et al in GB 2007162 (1979) and by Vaughtet al in U.S. Pat. No. 4,490,728. Both the aforementioned referenced inkjet printing techniques rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture in communication with the confined space onto a relevantprint media. Printing devices utilizing the electrothermal actuator aremanufactured by manufacturers such as Canon and Hewlett Packard.

[0010] As can be seen from the foregoing, many different types ofprinting technologies are available. Ideally, a printing technologyshould have a number of desirable attributes. These include inexpensiveconstruction and operation, high speed operation, safe and continuouslong term operation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction, operation, durability andconsumables.

SUMMARY OF THE INVENTION

[0011] There is disclosed herein an ink jet nozzle assembly including anozzle chamber having a nozzle, the chamber including a movable portionconfigured for movement to effect ejection of ink from the chamber viasaid nozzle, and a pair of actuating arms attached to or formedintegrally with the movable portion, the arms effecting movement of saidmovable portion as a result of one of said arms being periodicallyhotter than the other said arm in use.

[0012] There are many ways in which one of the arms can be made hotterthan the other in use. For example, the hotter arm could have less heatsinking than the other arm. The cold arm could be in cooling water,whereas the hot arm might not be in the water. The hotter arm might havelower mass than the colder arm. A greater current might be passedthrough one arm making it hotter than the other. The arm to be madehotter might have greater resistance than the other arm. More electricalpower might be applied to one arm, thus making it hotter than the other,or the arm to be made hotter might have more thermal insulation appliedto it.

[0013] There is further disclosed herein an ink jet nozzle assemblyincluding: a nozzle chamber having an inlet in fluid communication withan ink reservoir and a nozzle through which ink from the chamber can beejected;

[0014] the chamber including a fixed portion and a movable portionconfigured for relative movement in an ejection phase and alternaterelative movement in a refill phase;

[0015] a pair of spaced apart actuating arms connected with the movableportion and undergoing differential thermal expansion upon heating toeffect periodically said relative movement; and

[0016] the inlet being positioned and dimensioned relative to the nozzlesuch that ink is ejected preferentially from the chamber through thenozzle in droplet form during the ejection phase, and ink is alternatelydrawn preferentially into the chamber from the reservoir through theinlet during the refill phase.

[0017] Preferably the movable portion includes the nozzle and the fixedportion is mounted on a substrate.

[0018] Preferably the fixed portion includes the nozzle mounted on asubstrate and the movable portion includes an ejection paddle.

[0019] Preferably the arms extend between the paddle and the substrate.

[0020] Preferably the arms are located substantially within the chamber.

[0021] Alternately the arms are located substantially outside thechamber.

[0022] Preferably the fixed portion includes a slot a sidewall of thechamber through which the arms are connected to the paddle.

[0023] Preferably the arms are of substantially the same cross-sectionalprofile relative to one another.

[0024] Alternatively the arms are of differing cross-sectional profilerelative to one another.

[0025] Preferably the arms are heated simultaneously.

[0026] Preferably one arm is heated to a higher temperature than theother arm.

[0027] Preferably the arms are of substantially the same materialcomposition relative to one another.

[0028] Alternatively the arms are of substantially different materialcomposition relative to one another.

[0029] Preferably the arms are substantially parallel to one another.

[0030] Alternatively the arms are substantially non-parallel to oneanother.

[0031] Preferably the assembly is manufactured usingmicro-electro-mechanical systems (MEMS) techniques.

[0032] Preferably an effective volume of the chamber is reduced in saidejection phase and enlarged in said refill phase.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Notwithstanding any other forms which may fall within the scopeof the present invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

[0034]FIG. 1 illustrates a perspective view of an ink jet nozzlearrangement in accordance with the preferred embodiment;

[0035]FIG. 2 illustrates the arrangement of FIG. 1 when the actuator isin an activated position;

[0036]FIG. 3 illustrates an exploded perspective view of the majorcomponents of the preferred embodiment;

[0037]FIG. 4 provides a legend of the materials indicated in FIGS. 5 to16;

[0038] FIGS. 5 to 16 illustrate sectional views of the manufacturingsteps in one form of construction of an ink jet printhead nozzle;

[0039]FIG. 17 shows a three dimensional, schematic view of a nozzleassembly for an ink jet printhead in accordance with the invention;

[0040] FIGS. 18 to 20 show a three dimensional, schematic illustrationof an operation of the nozzle assembly of FIG. 17;

[0041]FIG. 21 shows a three dimensional view of a nozzle arrayconstituting an ink jet printhead;

[0042]FIG. 22 shows, on an enlarged scale, part of the array of FIG. 21;

[0043]FIG. 23 shows a three dimensional view of an ink jet printheadincluding a nozzle guard;

[0044]FIGS. 24a to 24 r show three-dimensional views of steps in themanufacture of a nozzle assembly of an ink jet printhead;

[0045]FIGS. 25a to 25 r show sectional side views of the manufacturingsteps;

[0046]FIGS. 26a to 26 k show layouts of masks used in various steps inthe manufacturing process;

[0047]FIGS. 27a to 27 c show three dimensional views of an operation ofthe nozzle assembly manufactured according to the method of FIGS. 24 and25; and

[0048]FIGS. 28a to 28 c show sectional side views of an operation of thenozzle assembly manufactured according to the method of FIGS. 24 and 25.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0049] In the preferred embodiment, there is provided an ink jetprinting system wherein each nozzle has a nozzle chamber having aslotted side wall through which is formed an actuator mechanism attachedto a vane within the nozzle chamber such that the actuator can beactivated to move the vane within the nozzle chamber to thereby causeejection of ink from the nozzle chamber.

[0050] Turning now to the figures, there is illustrated in FIG. 1 anexample of an ink jet nozzle arrangement 1 as constructed in accordancewith the preferred embodiment. The nozzle arrangement includes a nozzlechamber 2 normally filled with ink and an actuator mechanism 3 foractuating a vane 4 for the ejection of ink from the nozzle chamber 2 viaan ink ejection port 5.

[0051]FIG. 1 is a perspective view of the ink jet nozzle arrangement ofthe preferred embodiment in its idle or quiescent position. FIG. 2illustrates a perspective view after actuation of the actuator 3.

[0052] The actuator 3 includes two arms 6, 7. The two arms can be formedfrom titanium di-boride (TiB₂) which has a high Young's modulus andtherefore provides a large degree of bending strength. A current ispassed along the arms 6, 7 with the arm 7 having a substantially thickerportion along most of its length. The arm 7 is stiff but for in the areaof thinned portion 8 and hence the bending moment is concentrated in thearea 8. The thinned arm 6 is of a thinner form and is heated by means ofresistive heating of a current passing through the arms 6, 7. The arms6, 7 are interconnected with electrical circuitry via connections 10,11.

[0053] Upon heating of the arm 6, the arm 6 is expanded with the bendingof the arm 7 being concentrated in the area 8. This results in movementof the end of the actuator mechanism 3 which proceeds through a slot 19in a wall of the nozzle chamber 2. The bending further causes movementof vane 4 so as to increase the pressure of the ink within the nozzlechamber and thereby cause its subsequent ejection from ink ejection port5. The nozzle chamber 2 is refilled via an ink channel 13 (FIG. 3)formed in a wafer substrate 14. After movement of the vane 4, so as tocause the ejection of ink, the current to arm 6 is turned off whichresults in a corresponding back movement of the vane 4. The ink withinnozzle chamber 2 is then replenished by means of wafer ink supplychannel 13 which is attached to an ink supply formed on the back ofwafer 14. The refill can be by means of a surface tension reductioneffect of the ink within nozzle chamber 2 across ink ejection port 5.

[0054]FIG. 3 illustrates an exploded perspective view of the componentsof the ink jet nozzle arrangement.

[0055] Referring now specifically to FIG. 3, the preferred embodimentcan be constructed utilizing semiconductor processing techniques inaddition to micro machining and micro fabrication process technology(MEMS) and a full familiarity with these technologies is hereinafterassumed.

[0056] For a general introduction to a micro-electro mechanical system(MEMS) reference is made to standard proceedings in this field includingthe proceeding of the SPIE (International Society for OpticalEngineering) including volumes 2642 and 2882 which contain theproceedings of recent advances and conferences in this field.

[0057] The nozzles can preferably be constructed by constructing a largearray of nozzles on a single silicon wafer at a time. The array ofnozzles can be divided into multiple printheads, with each printheaditself having nozzles grouped into multiple colors to provide for fullcolor image reproduction. The arrangement can be constructed via theutilization of a standard silicon wafer substrate 14 upon which isdeposited an electrical circuitry layer 16 which can comprise a standardCMOS circuitry layer. The CMOS layer can include an etched portiondefining pit 17. On top of the CMOS layer is initially deposited aprotective layer (not shown) which comprise silicon nitride or the like.On top of this layer is deposited a sacrificial material which isinitially suitably etched so as to form cavities for the portion of thethermal actuator 3 and bottom portion of the vane 4, in addition to thebottom rim of nozzle chamber 2. These cavities can then be filled withtitanium diboride. Next, a similar process is used to form the glassportions of the actuator. Next, a further layer of sacrificial materialis deposited and suitably etched so as to form the rest of the vane 4 inaddition to a portion of the nozzle chamber walls to the same height ofvane 4.

[0058] Subsequently, a further sacrificial layer is deposited and etchedin a suitable manner so as to form the rest of the nozzle chamber 2. Thetop surface of the nozzle chamber is further etched so as to form thenozzle rim rounding the ejection port 5. Subsequently, the sacrificialmaterial is etched away so as to release the construction of thepreferred embodiment. It will be readily evident to those skilled in theart that other MEMS processing steps could be utilized.

[0059] Preferably, the thermal actuator and vane portions 3 and 4 inaddition to the nozzle chamber 2 are constructed from titaniumdi-boride. The utilization of titanium di-boride is standard in theconstruction of semiconductor systems and, in addition, its materialproperties, including a high Young's modulus, is utilized to advantagein the construction of the thermal actuator 3.

[0060] Further, preferably the actuator 3 is covered with a hydrophobicmaterial, such as Teflon, so as to prevent any leaking of the liquid outof the slot 19.

[0061] Further, as a final processing step, the ink channel can beetched through the wafer utilizing a high anisotropic silicon waferetch. This can be done as an anisotropic crystallographic silicon etch,or an anisotropic dry etch. A dry etch system capable of high aspectratio deep silicon trench etching such as the Surface Technology Systems(STS) Advance Silicon Etch (ASE) system is recommended for volumeproduction, as the chip size can be reduced over a wet etch. The wetetch is suitable for small volume production where a suitable plasmaetch system is not available. Alternatively, but undesirably, ink accesscan be around the sides of the printhead chips. If ink access is throughthe wafer higher ink flow is possible, and there is less requirement forhigh accuracy assembly. If ink access is around the edge of the chip,ink flow is severely limited, and the printhead chips must be carefullyassembled onto ink channel chips. This latter process is difficult dueto the possibility of damaging the fragile nozzle plate. If plasmaetching is used, the chips can be effectively diced at the same time.Separating the chips by plasma etching allows them to be spaced aslittle as 35 μm apart, increasing the number of chips on a wafer.

[0062] One form of detailed manufacturing process which can be used tofabricate monolithic ink jet print heads operating in accordance withthe principles taught by the present embodiment can proceed utilizingthe following steps:

[0063] 1. Using a double sided polished wafer, complete drivetransistors, data distribution, and timing circuits using a 0.5 micron,one poly, 2 metal CMOS process. Relevant features of the wafer at thisstep are shown in FIG. 5. For clarity, these diagrams may not be toscale, and may not represent a cross section though any single plane ofthe nozzle. FIG. 4 is a key to representations of various materials inthese manufacturing diagrams, and those of other cross referenced inkjet configurations.

[0064] 2. Etch oxide down to silicon or aluminum using Mask 1. This maskdefines the ink inlet, the heater contact vias, and the edges of theprinthead chips. This step is shown in FIG. 6.

[0065] 3. Deposit 1 micron of sacrificial material 21 (e.g. aluminum)

[0066] 4. Etch the sacrificial layer 21 using Mask 2, defining thenozzle chamber wall and the actuator anchor point. This step is shown inFIG. 7.

[0067] 5. Deposit 1 micron of heater material 22, for example titaniumnitride (TiN) or titanium diboride (TiB₂).

[0068] 6. Etch the heater material 22 using Mask 3, which defines theactuator loop and the lowest layer of the nozzle wall. This step isshown in FIG. 8.

[0069] 7. Wafer probe. All electrical connections are complete at thispoint, bond pads are accessible, and the chips are not yet separated.

[0070] 8. Deposit 1 micron of titanium nitride 23.

[0071] 9. Etch the titanium nitride 23 using Mask 4, which defines thenozzle chamber wall, with the exception of the nozzle chamber actuatorslot, and the paddle. This step is shown in FIG. 9.

[0072] 10. Deposit 8 microns of sacrificial material 24.

[0073] 11. Etch the sacrificial material 24 down to titanium nitride 23using Mask 5. This mask defines the nozzle chamber wall and the paddle.This step is shown in FIG. 10.

[0074] 12. Deposit a 0.5 micron conformal layer of titanium nitride 25and planarize down to the sacrificial layer using CMP.

[0075] 13. Deposit 1 micron of sacrificial material 26.

[0076] 14. Etch the sacrificial material 26 down to titanium nitride 25using Mask 6. This mask defines the nozzle chamber wall. This step isshown in FIG. 11.

[0077] 15. Deposit 1 micron of titanium nitride 27.

[0078] 16. Etch to a depth of (approx.) 0.5 micron using Mask 7. Thismask defines the nozzle rim 28. This step is shown in FIG. 12.

[0079] 17. Etch down to the sacrificial layer 26 using Mask 8. This maskdefines the roof of the nozzle chamber 2, and the port 5. This step isshown in FIG. 13.

[0080] 18. Back-etch completely through the silicon wafer 14 (with, forexample, an ASE Advanced Silicon Etcher from Surface Technology Systems)using Mask 9. This mask defines the ink inlets which are etched throughthe wafer 14. The wafer 14 is also diced by this etch. This step isshown in FIG. 14.

[0081] 19. Etch the sacrificial material 24. The nozzle chambers 2 arecleared, the actuators 3 freed, and the chips are separated by thisetch. This step is shown in FIG. 15.

[0082] 20. Mount the printheads in their packaging, which may be amolded plastic former incorporating ink channels which supply theappropriate color ink to the ink inlets at the back of the wafer.

[0083] 21. Connect the printheads to their interconnect systems. For alow profile connection with minimum disruption of airflow, TAB may beused. Wire bonding may also be used if the printer is to be operatedwith sufficient clearance to the paper.

[0084] 22. Hydrophobize the front surface of the printheads.

[0085] 23. Fill the completed printheads with ink 29 and test them. Afilled nozzle is shown in FIG. 16.

[0086] Referring now to FIG. 17 of the drawings, a nozzle assembly, inaccordance with a further embodiment of the invention is designatedgenerally by the reference numeral 110. An ink jet printhead has aplurality of nozzle assemblies 110 arranged in an array 114 (FIGS. 21and 22) on a silicon substrate 116. The array 114 will be described ingreater detail below.

[0087] The assembly 110 includes a silicon substrate or wafer 116 onwhich a dielectric layer 118 is deposited. A CMOS passivation layer 120is deposited on the dielectric layer 118.

[0088] Each nozzle assembly 110 includes a nozzle 122 defining a nozzleopening 124, a connecting member in the form of a lever arm 126 and anactuator 128. The lever arm 126 connects the actuator 128 to the nozzle122.

[0089] As shown in greater detail in FIGS. 18 to 20 of the drawings, thenozzle 122 comprises a crown portion 130 with a skirt portion 132depending from the crown portion 130. The skirt portion 132 forms partof a peripheral wall of a nozzle chamber 134 (FIGS. 18 to 20 of thedrawings). The nozzle opening 124 is in fluid communication with thenozzle chamber 134. It is to be noted that the nozzle opening 124 issurrounded by a raised rim 136 which “pins” a meniscus 138 (FIG. 18) ofa body of ink 140 in the nozzle chamber 134.

[0090] An ink inlet aperture 142 (shown most clearly in FIG. 22 of thedrawing) is defined in a floor 146 of the nozzle chamber 134. Theaperture 142 is in fluid communication with an ink inlet channel 148defined through the substrate 116.

[0091] A wall portion 150 bounds the aperture 142 and extends upwardlyfrom the floor portion 146. The skirt portion 132, as indicated above,of the nozzle 122 defines a first part of a peripheral wall of thenozzle chamber 134 and the wall portion 150 defines a second part of theperipheral wall of the nozzle chamber 134.

[0092] The wall 150 has an inwardly directed lip 152 at its free endwhich serves as a fluidic seal which inhibits the escape of ink when thenozzle 122 is displaced, as will be described in greater detail below.It will be appreciated that, due to the viscosity of the ink 140 and thesmall dimensions of the spacing between the lip 152 and the skirtportion 132, the inwardly directed lip 152 and surface tension functionas a seal for inhibiting the escape of ink from the nozzle chamber 134.

[0093] The actuator 128 is a thermal bend actuator and is connected toan anchor 154 extending upwardly from the substrate 116 or, moreparticularly, from the CMOS passivation layer 120. The anchor 154 ismounted on conductive pads 156 which form an electrical connection withthe actuator 128.

[0094] The actuator 128 comprises a first, active beam 158 arrangedabove a second, passive beam 160. In a preferred embodiment, both beams158 and 160 are of, or include, a conductive ceramic material such astitanium nitride (TiN).

[0095] Both beams 158 and 160 have their first ends anchored to theanchor 154 and their opposed ends connected to the arm 126. When acurrent is caused to flow through the active beam 158 thermal expansionof the beam 158 results. As the passive beam 160, through which there isno current flow, does not expand at the same rate, a bending moment iscreated causing the arm 126 and, hence, the nozzle 122 to be displaceddownwardly towards the substrate 116 as shown in FIG. 19 of thedrawings. This causes an ejection of ink through the nozzle opening 124as shown at 162 in FIG. 19 of the drawings. When the source of heat isremoved from the active beam 158, i.e. by stopping current flow, thenozzle 122 returns to its quiescent position as shown in FIG. 20 of thedrawings. When the nozzle 122 returns to its quiescent position, an inkdroplet 164 is formed as a result of the breaking of an ink droplet neckas illustrated at 166 in FIG. 20 of the drawings. The ink droplet 164then travels on to the print media such as a sheet of paper. As a resultof the formation of the ink droplet 164, a “negative” meniscus is formedas shown at 168 in FIG. 20 of the drawings. This “negative” meniscus 168results in an inflow of ink 140 into the nozzle chamber 134 such that anew meniscus 138 (FIG. 18) is formed in readiness for the next ink dropejection from the nozzle assembly 110.

[0096] Referring now to FIGS. 21 and 22 of the drawings, the nozzlearray 114 is described in greater detail. The array 114 is for a fourcolor printhead. Accordingly, the array 114 includes four groups 170 ofnozzle assemblies, one for each color. Each group 170 has its nozzleassemblies 110 arranged in two rows 172 and 174. One of the groups 170is shown in greater detail in FIG. 22 of the drawings.

[0097] To facilitate close packing of the nozzle assemblies 110 in therows 172 and 174, the nozzle assemblies 110 in the row 174 are offset orstaggered with respect to the nozzle assemblies 110 in the row 172.Also, the nozzle assemblies 110 in the row 172 are spaced apartsufficiently far from each other to enable the lever arms 126 of thenozzle assemblies 110 in the row 174 to pass between adjacent nozzles122 of the assemblies 110 in the row 172. It is to be noted that eachnozzle assembly 110 is substantially dumbbell shaped so that the nozzles122 in the row 172 nest between the nozzles 122 and the actuators 128 ofadjacent nozzle assemblies 110 in the row 174.

[0098] Further, to facilitate close packing of the nozzles 122 in therows 172 and 174, each nozzle 122 is substantially hexagonally shaped.

[0099] It will be appreciated by those skilled in the art that, when thenozzles 122 are displaced towards the substrate 116, in use, due to thenozzle opening 124 being at a slight angle with respect to the nozzlechamber 134 ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 21 and 22 of the drawingsthat the actuators 128 of the nozzle assemblies 110 in the rows 172 and174 extend in the same direction to one side of the rows 172 and 174.Hence, the ink droplets ejected from the nozzles 122 in the row 172 andthe ink droplets ejected from the nozzles 122 in the row 174 areparallel to one another resulting in an improved print quality.

[0100] Also, as shown in FIG. 21 of the drawings, the substrate 116 hasbond pads 176 arranged thereon which provide the electrical connections,via the pads 156, to the actuators 128 of the nozzle assemblies 110.These electrical connections are formed via the CMOS layer (not shown).

[0101] Referring to FIG. 23 of the drawings, a development of theinvention is shown. With reference to the previous drawings, likereference numerals refer to like parts, unless otherwise specified.

[0102] In this development, a nozzle guard 180 is mounted on thesubstrate 116 of the array 114. The nozzle guard 180 includes a bodymember 182 having a plurality of passages 184 defined therethrough. Thepassages 184 are in register with the nozzle openings 124 of the nozzleassemblies 110 of the array 114 such that, when ink is ejected from anyone of the nozzle openings 124, the ink passes through the associatedpassage 184 before striking the print media.

[0103] The body member 182 is mounted in spaced relationship relative tothe nozzle assemblies 110 by limbs or struts 186. One of the struts 186has air inlet openings 188 defined therein.

[0104] In use, when the array 114 is in operation, air is chargedthrough the inlet openings 188 to be forced through the passages 184together with ink travelling through the passages 184.

[0105] The ink is not entrained in the air as the air is charged throughthe passages 184 at a different velocity from that of the ink droplets164. For example, the ink droplets 164 are ejected from the nozzles 122at a velocity of approximately 3 m/s. The air is charged through thepassages 184 at a velocity of approximately 1 m/s.

[0106] The purpose of the air is to maintain the passages 184 clear offoreign particles. A danger exists that these foreign particles, such asdust particles, could fall onto the nozzle assemblies 110 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 180 this problem is, to a large extent, obviated.

[0107] Referring now to FIGS. 24 to 26 of the drawings, a process formanufacturing the nozzle assemblies 110 is described.

[0108] Starting with the silicon substrate or wafer 116, the dielectriclayer 118 is deposited on a surface of the wafer 116. The dielectriclayer 118 is in the form of approximately 1.5 microns of CVD oxide.Resist is spun on to the layer 118 and the layer 118 is exposed to mask200 and is subsequently developed.

[0109] After being developed, the layer 118 is plasma etched down to thesilicon layer 116. The resist is then stripped and the layer 118 iscleaned. This step defines the ink inlet aperture 142.

[0110] In FIG. 24b of the drawings, approximately 0.8 microns ofaluminum 202 is deposited on the layer 118. Resist is spun on and thealuminum 202 is exposed to mask 204 and developed. The aluminum 202 isplasma etched down to the oxide layer 118, the resist is stripped andthe device is cleaned. This step provides the bond pads andinterconnects to the ink jet actuator 128. This interconnect is to anNMOS drive transistor and a power plane with connections made in theCMOS layer (not shown).

[0111] Approximately 0.5 microns of PECVD nitride is deposited as theCMOS passivation layer 120. Resist is spun on and the layer 120 isexposed to mask 206 whereafter it is developed. After development, thenitride is plasma etched down to the aluminum layer 202 and the siliconlayer 116 in the region of the inlet aperture 142. The resist isstripped and the device cleaned.

[0112] A layer 208 of a sacrificial material is spun on to the layer120. The layer 208 is 6 microns of photo-sensitive polyimide orapproximately 4 μm of high temperature resist. The layer 208 issoftbaked and is then exposed to mask 210 whereafter it is developed.The layer 208 is then hardbaked at 400° C. for one hour where the layer208 is comprised of polyimide or at greater than 300° C. where the layer208 is high temperature resist. It is to be noted in the drawings thatthe pattern-dependent distortion of the polyimide layer 208 caused byshrinkage is taken into account in the design of the mask 210.

[0113] In the next step, shown in FIG. 24e of the drawings, a secondsacrificial layer 212 is applied. The layer 212 is either 2 μm ofphoto-sensitive polyimide which is spun on or approximately 1.3 μm ofhigh temperature resist. The layer 212 is softbaked and exposed to mask214. After exposure to the mask 214, the layer 212 is developed. In thecase of the layer 212 being polyimide, the layer 212 is hardbaked at400° C. for approximately one hour. Where the layer 212 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

[0114] A 0.2 micron multi-layer metal layer 216 is then deposited. Partof this layer 216 forms the passive beam 160 of the actuator 128.

[0115] The layer 216 is formed by sputtering 1,000Å of titanium nitride(TiN) at around 300° C. followed by sputtering 50Å of tantalum nitride(TaN). A further 1,000Å of TiN is sputtered on followed by 50Å of TaNand a further 1,000Å of TiN.

[0116] Other materials which can be used instead of TiN are TiB₂, MoSi₂or (Ti, Al)N.

[0117] The layer 216 is then exposed to mask 218, developed and plasmaetched down to the layer 212 whereafter resist, applied for the layer216, is wet stripped taking care not to remove the cured layers 208 or212.

[0118] A third sacrificial layer 220 is applied by spinning on 4 μm ofphoto-sensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 220 is softbaked whereafter it is exposed to mask 222.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 220 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 220 comprisesresist.

[0119] A second multi-layer metal layer 224 is applied to the layer 220.The constituents of the layer 224 are the same as the layer 216 and areapplied in the same manner. It will be appreciated that both layers 216and 224 are electrically conductive layers.

[0120] The layer 224 is exposed to mask 226 and is then developed. Thelayer 224 is plasma etched down to the polyimide or resist layer 220whereafter resist applied for the layer 224 is wet stripped taking carenot to remove the cured layers 208, 212 or 220. It will be noted thatthe remaining part of the layer 224 defines the active beam 158 of theactuator 128.

[0121] A fourth sacrificial layer 228 is applied by spinning on 4 μm ofphoto-sensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 228 is softbaked, exposed to the mask 230 and is thendeveloped to leave the island portions as shown in FIG. 9k of thedrawings. The remaining portions of the layer 228 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

[0122] As shown in FIG. 24l of the drawing a high Young's modulusdielectric layer 232 is deposited. The layer 232 is constituted byapproximately 1 μm of silicon nitride or aluminum oxide. The layer 232is deposited at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220, 228. The primary characteristicsrequired for this dielectric layer 232 are a high elastic modulus,chemical inertness and good adhesion to TiN.

[0123] A fifth sacrificial layer 234 is applied by spinning on 2 μm ofphoto-sensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 234 is softbaked, exposed to mask 236 and developed.The remaining portion of the layer 234 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

[0124] The dielectric layer 232 is plasma etched down to the sacrificiallayer 228 taking care not to remove any of the sacrificial layer 234.

[0125] This step defines the nozzle opening 124, the lever arm 126 andthe anchor 154 of the nozzle assembly 110.

[0126] A high Young's modulus dielectric layer 238 is deposited. Thislayer 238 is formed by depositing 0.2 μm of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220 and 228.

[0127] Then, as shown in FIG. 24p of the drawings, the layer 238 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from all of the surface except the sidewalls of the dielectric layer 232 and the sacrificial layer 234. Thisstep creates the nozzle rim 136 around the nozzle opening 124 which“pins” the meniscus of ink, as described above.

[0128] An ultraviolet (UV) release tape 240 is applied. 4 μm of resistis spun on to a rear of the silicon wafer 116. The wafer 116 is exposedto mask 242 to back etch the wafer 116 to define the ink inlet channel148. The resist is then stripped from the wafer 116.

[0129] A further UV release tape (not shown) is applied to a rear of thewafer 16 and the tape 240 is removed. The sacrificial layers 208, 212,220, 228 and 234 are stripped in oxygen plasma to provide the finalnozzle assembly 110 as shown in FIGS. 24r and 25 r of the drawings. Forease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 17 of the drawings to indicatethe relevant parts of the nozzle assembly 110. FIGS. 27 and 28 show theoperation of the nozzle assembly 110, manufactured in accordance withthe process described above with reference to FIGS. 24 and 25, and thesefigures correspond to FIGS. 18 to 20 of the drawings.

[0130] The presently disclosed ink jet printing technology ispotentially suited to a wide range of printing system including: colorand monochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters high speed pagewidth printers, notebook computers with in-builtpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic“minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademarkof the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

[0131] It would be appreciated by a person skilled in the art thatnumerous variations and/or modifications any be made to the presentinvention as shown in the specific embodiment without departing from thespirit or scope of the invention as broadly described. The presentembodiment is, therefore, to be considered in all respects to beillustrative and not restrictive.

We claim:
 1. An ink jet nozzle assembly including a nozzle chamberhaving a nozzle, the chamber including a movable portion configured formovement to effect ejection of ink from the chamber via said nozzle, anda pair of actuating arms attached to or formed integrally with themovable portion, the arms effecting movement of said movable portion asa result of one of said arms being periodically hotter than the othersaid arm in use.
 2. An ink jet nozzle assembly including: a nozzlechamber having an inlet in fluid communication with an ink reservoir anda nozzle through which ink from the chamber can be ejected; the chamberincluding a fixed portion and a movable portion configured for relativemovement in an ejection phase and alternate relative movement in arefill phase; a pair of spaced apart actuating arms connected with themovable portion and undergoing differential thermal expansion uponheating to effect periodically said relative movement; and the inletbeing positioned and dimensioned relative to the nozzle such that ink isejected preferentially from the chamber through the nozzle in dropletform during the ejection phase, and ink is alternately drawnpreferentially into the chamber from the reservoir through the inletduring the refill phase.
 3. An assembly according to claim 2 wherein themovable portion includes the nozzle and the fixed portion is mounted ona substrate.
 4. An assembly according to claim 2 wherein the fixedportion includes the nozzle mounted on a substrate and the movableportion includes an ejection paddle.
 5. An assembly according to claim 4wherein the arms extend between the paddle and the substrate.
 6. Anassembly according to claim 2 wherein the arms are located substantiallywithin the chamber.
 7. An assembly according to claim 4 wherein the armsare located substantially outside the chamber.
 8. An assembly accordingto claim 7 wherein the fixed portion includes a slot a sidewall of thechamber through which the arms are connected to the paddle.
 9. Anassembly according to claim 2 wherein the arms are of substantially thesame cross-sectional profile relative to one another.
 10. An assemblyaccording to claim 2 wherein the arms are of differing cross-sectionalprofile relative to one another.
 11. An assembly according to claim 2wherein the arms are heated simultaneously.
 12. An assembly according toclaim 2 wherein one arm is heated to a higher temperature than the otherarm.
 13. An assembly according to claim 2 wherein the arms are ofsubstantially the same material composition relative to one another. 14.An assembly according to claim 2 wherein the arms are of substantiallydifferent material composition relative to one another.
 15. An assemblyaccording to claim 2 wherein the arms are substantially parallel to oneanother.
 16. An assembly according to claim 2 wherein the arms aresubstantially non-parallel to one another.
 17. An assembly according toclaim 2 , manufactured using micro-electro-mechanical systems (MEMS)techniques.
 18. An assembly according to claim 2 wherein an effectivevolume of the chamber is reduced in said ejection phase and enlarged insaid refill phase.